Hey Jeremy,
I’m sorry I’m currently not sure what the issue is as when you convert to Pro, your Cornerstone built pages would not be opened with Pro’s Content Builder. Pro will also deactivate Cornerstone as that is no longer needed.
Do you mean that the pages you previously made using Cornerstone can no longer be edited using Pro’s Content Builder?
Regarding the “This preview could not load due to iframe response…” error, I’ve answered it in your previous thread. Please read my answer here: https://theme.co/apex/forum/t/unable-to-edit-certain-pages-using-pro/67923/6?u=christian_y
Please do not post similar questions multiple times as that is unfair to other customers. We assure you that we will answer your questions. Please just kindly wait as we receive high a lot of questions sometimes.
Thanks.